Need help with physics

1)define clearly the principle of conservation of momentum and apply this to solve the following problem:
A man weighing 730N stands in the middle of a frozen pound of a radius 5.9m. he is unable to get to the other side becuase of lack of friction between his shoes and the ice. to overcome this problem, he throws his 1.2kg book horizontally towards the north shore at a speed of 5m/s. how long does it take him to reach the south shore?

2) a 40g ball travelling to the right , at 30 cm/s collides, in a stright line, with 80g ball that is at rest. if the collision is perectily elastic, what is the velocity of each ball after collision?

plz could you help me with this im completly a newbie to physics, so please could you help.

None of what you wrote makes any sense. Let m1 be the mass of the man, let m2 be the mass of the book (both of these should be in kg). So v2 is the speed with which the man throws the book. All you have to do is substitute those values into the momentum equation, and solve for v1.

This is quite sloppy. 750N does not "equal" 76.53kg. They don't have the same units, so they certainly cannot be equal to each other.

m1V1 + m2 * V2

76.53 * 0 + 1.2 * 5 = 6

Why are you plugging in 0 for V1? The whole point of the problem is for you to solve for V1. We don't know what it is yet, but it obvioulsy isn't zero. Conservation of momentum tells us that the forward momentum of the book is going to be equal in magnitude to the backward momentum of the man.